1. Field of the Invention
The present invention relates to a secondary battery for use in portable electronic apparatus, etc. More particularly, the present invention relates to a battery which can be in a thin form and an adhesive for use in the battery.
2. Description of the Related Art
There has been a very great demand for the reduction of the size and weight of portable electronic apparatus. The improvement of properties and the reduction of the size of batteries to be used therefor are indispensable for the accomplishment of these demands. To this end, the development of various batteries and the improvement of the properties of batteries are under way. Requirements for batteries are high voltage supply, high energy density, high reliability, arbitrariness of shape, etc. A lithium ion battery is a secondary battery which can be expected to realize the highest voltage and largest energy density in conventional batteries, and its improvement is still under way on an extensive scale.
A lithium ion battery comprises as essential elements a positive electrode plate, a negative electrode plate, and an ionically-conducting layer provided interposed therebetween. A lithium ion battery which has been put into practical use comprises as a positive electrode one obtained by applying a powder of lithium cobalt oxide or the like as an active material to a collector, and then forming the coated material into a plate and as a negative electrode one obtained by applying a powdered carbon-based material as an active material to a collector, and then forming the coated material into a plate. As the ionically-conducting layer there is used a porous film of polyethylene or polypropylene impregnated with a nonaqueous electrolyte which acts as a separator interposed between the positive electrode and the negative electrode.
In the conventional lithium ion batteries, it is necessary that all the surfaces of the positive electrode, the separator and the negative electrode are kept in contact with each other under an external pressure given by a rigid casing made of a metal or the like to keep these elements in electrical contact with each other as disclosed in JP-A-8-83608 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d).
Further, JP-A-5-159802 for secondary solid battery discloses a production process which comprises binding an electrolyte layer to an electrode material layer with a thermoplastic resin binder under heating to integrate the battery elements in one. In this case, the integration of the electrode and the electrolyte makes it possible to maintain electrical contact therebetween, eliminating the necessity of applying an external pressure to the battery when it works properly.
As a thin film battery there is known one comprising as an ionically-conducting material a polymer gel as described in U.S. Pat. No. 5,460,904. In this thin film battery, a copolymer of polyvinylidene fluoride and hexafluoropropylene is used as a polymer gel to integrate the positive electrode and the negative electrode in one.
The conventional battery described in JP-A-8-83608 is disadvantageous in that a rigid casing made of a metal or the like which can withstand an external pressure must be used to keep the electrode layer and the electrolyte layer in full electrical contact with each other. As a result, the casing, which is a portion other than the power-generating portion, accounts for a large portion of the battery in volume and weight, making it difficult to form a battery having a large energy density.
Further, the secondary solid battery disclosed in JP-A-5-159802 employs a solid binder to cover the electrode-electrolyte interface and thus is disadvantageous as compared with the foregoing type of a battery comprising a liquid electrolyte in a casing which can withstand an external pressure from the standpoint of the electrical conductivity of the electrode-electrolyte interface. If any used, no binders having an electrical conductivity equal to or higher than that of the liquid electrolyte have been generally found, making it impossible to provide an ionic conductivity equal to that of the battery comprising a liquid electrolyte.
Moreover, the thin film battery comprising a polyvinylidene fluoride disclosed in U.S. Pat. No. 5,460,904 is disadvantageous in that since the polyvinylidene fluoride copolymer is thermoplastic, its adhesive strength can be easily affected by temperature. In particular, at high temperatures, the polyvinylidene fluoride copolymer shows a drop of adhesive strength that causes peeling between the electrode and the separator, making it possible to accomplish the desired battery properties. The foregoing thin film battery is also disadvantageous in that it requires a complicated process. For example, the polyvinylidene fluoride copolymer ionically conductive must previously comprise a plasticizer incorporated therein to render itself ionically conductive. The copolymer is then formed into a predetermined shape. The plasticizer is then extracted with an organic solvent.
The present invention has been worked out to eliminate the foregoing problems. An object of the present invention is to provide an adhesive for battery which can easily form an electrode body having a good electrical contact between an electrode and an electrolyte within a wide temperature range free of rigid casing capable of withstanding an external pressure by connecting an electrode layer to an electrolyte layer, a battery formed by such an adhesive for battery, and a process for the production of such a battery.
The present invention relates to an adhesive for battery for adhering an electrode to a separator, characterized in that said adhesive contains at least one organic vinyl compound having two or more vinyl groups per molecule and comprises a a volatile organic solvent.
A first aspect of the adhesive for battery used for adhering an electrode to a separator of the present invention is an adhesive, which contains at least one organic vinyl compound having two or more vinyl groups per molecule and a volatile organic solvent.
A second aspect of the adhesive is an adhesive according to the first aspect, which further contains a reaction catalyst.
A third aspect of the adhesive is an adhesive according to the second aspect, which further contains a thermoplastic resin.
A fourth aspect of the adhesive is an adhesive according to the first aspect, wherein said organic vinyl compound having two or more vinyl groups per molecule is selected from the group consisting of an acrylic ester and methacrylic ester.
A fifth aspect of the adhesive is an adhesive according to the fourth aspect, which comprises in addition to said organic vinyl compound having two or more vinyl groups per molecule at least one organic vinyl compound containing one vinyl group per molecule.
A sixth aspect of the adhesive is an adhesive according to the third aspect, wherein said thermoplastic resin comprises at least one of a polyacrylic ester and polymethacrylic ester.
A seventh aspect of the battery of the present invention is a battery, which comprises an electrode laminate having:
a positive electrode;
a negative electrode;
a separator which is arranged between said positive electrode and negative electrode and keeps an electrolytic solution; and
an adhesive resin layer which bonds said positive electrode and said negative electrode to said separator,
wherein said adhesive resin layer contains at least one organic vinyl compound having at least two vinyl groups per molecule and a volatile organic solvent.
A eighth aspect of the battery is a battery according to the seventh aspect, wherein each of said positive electrode and negative electrode comprises a collector and an electrode active material layer formed on the collector, and
adhesive strength between the active material layer and the separator is not smaller than that between the active material layer and the collector.
A ninth aspect of the battery is a battery according to the seventh aspect, wherein said battery has a plurality of electrode laminates.
A tenth aspect of the battery is a battery according to the ninth aspect, wherein said plurality of electrode laminates are arranged by alternately interposing positive electrodes and negative electrodes between a plurality of cut separators one by one.
An eleventh aspect of the battery is a battery according to the ninth aspect, wherein said plurality of electrode laminates are arranged by alternately interposing positive electrodes and negative electrodes between the gap of a wound separator one by one.
A twelfth aspect of the battery is a battery according to the ninth aspect, wherein said plurality of electrode laminates are arranged by alternately interposing positive electrodes and negative electrodes between the gap of a pair of folded separators.
A thirteenth aspect of the method of fabricating a battery is a method of present invention, which comprises the steps of:
coating an adhesive contains at least one organic vinyl compound having at least two vinyl groups per molecule and a volatile organic solvent on at least one of a separator and each of negative and positive electrodes to be adhered each other;
laminating a positive electrode and a negative electrode on the both surfaces of the separator respectively to form a electrode laminate;
curing the adhesive by heating the electrode laminate so that said volatile organic solvent is evaporated off said adhesive.
A fourteenth aspect of the method is a method according to the thirteenth aspect, wherein said adhesive further contains a catalyst.
A fifteenth aspect of the method is a method according to the thirteenth aspect, wherein, wherein said adhesive further contains a thermoplastic resin.